Vacuum process chambers are often employed in manufacturing to provide a vacuum environment for tasks such as semiconductor wafer fabrication, electron microscopy, gas chromatography, and others. Such chambers are typically achieved by attaching a vacuum pump to the vacuum process chamber by a vacuum connection such as a flange and a conduit. The vacuum pump operates to remove substantially all of the molecules from the process chamber, therefore creating a vacuum environment.
A cryogenic vacuum pump, known as a cryopump, employs a refrigeration mechanism to achieve low temperatures that will cause many gases to condense onto a surface cooled by the refrigeration mechanism. One type of cryopump is disclosed in U.S. Pat. No. 5,862,671, issued Jan. 26, 1999 and assigned to the assignee of the present application. Such a cryopump uses a two-stage helium driven refrigerator to cool a cold finger to near 10 degrees Kelvin(K.). Another type of cryopump, often referred to as a water pump is disclosed in U.S. Pat. No. 5,887,438, issued Mar. 30, 1999 and also assigned to the assignee of the present application. A cryogenic water pump is typically employed in conjunction with a turbomolecular pump, and is also used to condense gases onto a helium cooled surface, or cryogenic array, which is cooled to around 100K.
Since the cryogenic arrays are cooled to very low temperatures, heat flow to the cryogenically cooled surface is ideally minimized. Undesired heat increases the time required to cool down the pump, increases the helium consumption of the pump, and influences the minimum temperature the cryopump achieves.
Note that both a cryopump and a waterpump, as disclosed herein, employ one or more refrigerant-cooled surfaces for condensing gases for the purpose of removing the gases from a closed environment such as a process chamber. A waterpump, for example, may be considered functionally equivalent to a cryopump having a single refrigerant-cooled surface, or stage. Accordingly, both a cryopump and a waterpump may benefit from radiation absorption as disclosed herein and therefore, the term “cryopump” may hereinafter be taken to imply either a cryopump or a waterpump.
A radiation shield may be employed around the cryogenic array to minimize the thermal load on the cryogenic array. Such a radiation shield may take the form of an enclosure around the cryogenic array, and may include louvers or chevrons to allow fluid communication with the vacuum process chamber. Louvers and chevrons, however, can interfere with the fluid communication, or gaseous flow, from the vacuum process chamber, decreasing flow rate and efficiency, and, therefore, increasing the time required to achieve the desired vacuum state.